The present invention relates to a vehicle suspension system, and in particular to a heavy duty, walking beam-type suspension system.
A variety of vehicle suspension units have been developed for vehicles that include two or more pairs of drive wheels. These suspension systems include single, tandem and tridem suspension systems, as well as equalizing or walking beam-type systems. Walking beam type systems, as described in more detail below, typically include a plurality of linkage arms cooperating to form a parallelogram, wherein one of the members, an equalizing beam, pivotally connects a pair of associated axles. A suspension unit is then supported between the associated frame of the supported vehicle and a midpoint of each equalizing beam. The suspension units typically include a plurality of leaf springs pivotally connected to the frame at a first end, and slidingly connected to the frame at a second end. Other variations of the walker beam-type suspension systems have included the use of a plurality of air springs as a replacement to the plurality of leaf springs.
Heretofore, these systems have proven inadequate to simultaneously provide acceptable load support and acceptable ride comfort. Specifically, the systems utilizing leaf springs provide adequate load support, however fail to provide sufficient ride comfort. More specifically, while these systems provide sufficient longitudinal roll stability to the associated vehicle frame, the leaf springs within these systems dictate a spring constant that remains consistent regardless of the load being supported. The result is a fixed rate suspension system, thereby creating a relatively rougher ride as the load on the frame is reduced. On the other hand, systems utilizing air cylinders provide adequate ride comfort; however, fail to provide sufficient longitudinal roll stability. Specifically, these systems are inherently variable rate devices, as the pressure within the air cylinders may be changed, thereby allowing the ride comfort to be maximized. However, these systems have failed to provide adequate longitudinal roll stability.
A vehicle suspension system is desired that simultaneously maximizes ride comfort for the operator of the associated vehicle, and maximizes longitudinal roll stability of the frame of the vehicle.